Synaptic vesicles purified from rat or cow brain in my preliminary studies are enriched in at least two synaptic vesicle-specific proteins identified by others and five additional major proteins that do not appear to have been studied previously. The functions of these proteins are not known, although it seems probable that some of the regulated interactions of synaptic vesicles with other neuronal elements that occur during delivery of these organelles to the synapse and their subsequent participation in neurotransmission are mediated by major synaptic vesicle proteins. The studies proposed here will probe structural and functional interactions among the synaptic vesicle proteins and between these proteins and other components of the synapse. Several experimental approaches will be taken. These include (1) covalent crosslinking and immunoprecipitation to elucidate interactions of the synaptic vesicle proteins within supramolecular complexes on the vesicle surface; (2) immunoprecipitation to determine the distributions of major proteins in synaptic vesicle subpopulations; (3) nerve crush experiments to assess anterograde and/or retrograde axonal transport of synaptic vesicle proteins; (4) immunochemical and axonal transport studies of a protein apparently specific to free but not recycling synaptic vesicle membranes; and (5) binding studies of synaptic vesicle proteins with presynaptic membrane or lipid bilayer components potentially involved in exocytosis. These studies aim to contribute to an understanding of the molecular mechanisms of transmitter release at mammalian synapses.